This invention is generally directed to processes for the preparation of developer compositions, especially liquid developers with excellent transfer efficiencies. More specifically, the present invention is directed to a process for the preparation of liquid developer compositions containing dyed polymeric particles with an average diameter of from about 2 to about 6 microns which comprises initially formulating a latex dispersion, thereafter dyeing the dispersion, and subsequently adding to the resulting dispersion components such as charge directors. Thus, in one important embodiment of the present invention there is provided a process for the preparation of liquid ink compositions with excellent transfer efficiencies, exceeding 80 percent (percent by weight of the ink composition developed on the photoreceptor and transferred, for example, to paper) or greater, which comprises the formation in a solvent mixture of a latex dispersion by polymerization, thereafter dyeing the product, and subsequently generating a liquid ink by adding thereto components such as charge directors. The liquid inks of the present invention can be selected for the development of images in various processes, including the liquid development process as described in U.S. Pat. No. 3,084,043, the disclosure of which is totally incorporated herein by reference; xerographic processes, electrographic recording, electrostatic printing, and facsimile systems; color proofing processes; and the process as illustrated in Savin British Patent Publication No. 2,169,416, published July 9, 1986, the disclosure of which is totally incorporated herein by reference.
Development of electrostatic latent images with liquid developer compositions comprised of, for example, a dispersion of pigments in a liquid hydrocarbon is known. In these methods, the electrostatic latent image, which is usually formulated on a single sheet of photoconductive paper, such as zinc oxide, is transported through a bath of the aforementioned liquid developer. Contact with the liquid developer causes the charged pigment particles present therein to migrate through the liquid to the zinc oxide sheet in the configuration of a charged image. Thereafter, the sheet is withdrawn from the liquid developer bath with the charged pigment particles adhering to the electrostatic latent image in image configuration. The thin film of residual developer remaining on the surface of the sheet is then evaporated within a relatively short time period, usually less than 5 seconds. Also, the marking pigment particles may be fixed to the sheet by heat, for example, in image configuration.
There are disclosed in U.S. Pat. No. 3,554,946 liquid developers for electrophotography comprised of a carrier liquid consisting of a hydrocarbon, negatively electrostatically charged toner particles dispersed in the carrier liquid, and a pigment therein such as carbon black, aniline black, prussian blue, phthalocyanine red, and cadmium yellow. In accordance with the teachings of this patent, a copolymer is coated on the surface of the pigment particles for the primary purpose of imparting a negative electrostatic charge to these particles. Other patents disclosing similar liquid developer compositions include U.S. Pat. Nos. 3,623,986; 3,625,897; 3,900,412; 3,976,583; 4,081,391 and 3,900,412. In the '412 patent there is specifically disclosed a stable developer comprised of a polymer core with a steric barrier attached to the surface of the polymer selected. In column 15 of this patent there are disclosed colored liquid developers by selecting pigments or dyes, and physically dispersing them by ball milling or high shear mixing. Attempts to obtain useful color liquid developer compositions by the ball milling process described have been substantially ineffective, particularly with respect to obtaining developed images of acceptable optical density in that, for example, the desired size for the latex particles is from 0.2 to 0.3 micron in diameter; and with ball milling techniques it is very difficult to provide a dispersion of carbon black or other pigment particles much smaller in size than about 0.7 to about 0.8 micron. Consequently, the addition of carbon black pigment particles, for example, to latex particles with a diameter of 0.2 to 0.3 micron, while ball milling would result in relatively small latex particles residing on the surface of the pigment particles. In contrast with the invention of the present application, there are obtained dyed polymer particles with an average diameter of from about 2 to about 6 microns permitting high transfer efficiencies since these larger particles do not migrate from the image during transfer as is the situation with submicron particles, and also the larger particles are not as strongly held to the photoreceptor surface.
Additionally, there are described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with submicron size marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
In addition, there are illustrated in the aforementioned British Patent Publication No. 2,169,416 liquid developer compositions comprising toner particles associated with a pigment dispersed in a nonpolar liquid, and wherein the toner particles are formulated with a plurality of fibers or tendrils from a thermoplastic polymer, and carry a charge of polarity opposite to the polarity of the latent image. These toners apparently permit in some instances excellent transfer efficiencies, however, they are difficult to prepare, batch to batch reproducibility is difficult to obtain; and further in some instances the resulting inks do not possess acceptable transfer of the image. It is believed that some of the aforementioned disadvantages occur since the particles are prepared by an attrition process, where the particle size and size distribution is difficult to control as compared to a chemical process.
Furthermore, there is illustrated in copending U.S. application Ser. No. 846,164, entitled Black Liquid Developer Composition, the disclosure of which is totally incorporated herein by reference, stable black submicron liquid developer comprised of an insulating liquid medium having dispersed therein black marking particles comprised of a thermoplastic resin core which is substantially insoluble in the dispersion medium, and chemically or physically anchored to the resin core an amphipathic block or graft copolymer steric stabilizer which is soluble in the dispersion medium; and wherein dyes comprised of a specific mixture are imbibed in the thermoplastic resin core with the mixture of dyes being dispersible at the molecular level, and therefore soluble in the thermoplastic resin core and insoluble in the dispersion medium.
Other patents of interest include U.S. Pat. No. 4,210,805, which discloses toner particles prepared by adding a solvent solution of polyvinylcarbazole to Isopar.RTM. wherein the diameter of the particles is a function of the ratio of solvent to Isopar.RTM., reference column 8; U.S. Pat. No. 4,032,463 which illustrates that the ratio of toluene to Isopar.RTM. effects toner resin particle size; and U.S. Pat. No. 3,766,072 which appears to disclose that resin solvency in the vehicle effects the particle size. Also, in the '463 and '072 patents it is indicated that a solvency increase of the dispersion medium provides a larger final size particle. This occurs, it is believed, because one of the liquids used in formulating such developers is a solvent for the resin that is used. Consequently, the particle will be swollen by the entrapped solvent in the particle yielding a larger particle size. Also, in the polymerization process changing the solvent/nonsolvent ratio of the dispersion medium changes the kinetics and thus the mechanism by which particles are formed. With latex particle polymerization, usually only submicron size particles are envisioned, reference for example "Dispersion Polymerization in Organic Media", ed. K. E. J. Barret, Academic Press, 1975.
Although the above described liquid inks and the processes thereof are suitable for their intended purposes, there remains a need for simple processes that will enable liquid developers containing dyed polymeric particles with a size diameter of from about 2 to about 6 microns thereby permitting the advantages illustrated herein. More specifically, there is a need for processes for obtaining liquid developers containing dyed polymeric particles with a size diameter of from about 2 to about 6 microns, which developers possess superior transfer efficiencies, and desirable conductivity values. There also is a need for colored liquid developers containing dyed polymeric particles with a size diameter of from about 2 to about 6 microns, which possess many of the aforementioned characteristics. Additionally, there is a need for economical liquid developer compositions that permit images of excellent resolution in a number of known imaging processes, including those illustrated in U.S. Pat. No. 3,084,043. Moreover, there is a need for processes for liquid developers wherein the colorants selected are suitable dispersed thus enabling black, or colored images of excellent resolution. Further, there remains a need for liquid developer processes wherein there is included therein certain steric stabilizers that stabilize the developer particles, and wherein these developers permit wetting of the photoreceptor surface thus permitting transfer efficiencies of 80 percent or greater.